Shape-controlled conversion of β-Sn nanocrystals into intermetallic M-Sn (M = Fe, Co, Ni, Pd) nanocrystals

The ability to control the shape of metal nanocrystals is critical to applications such as catalysis, magnetism, and plasmonics. Despite significant advances in controlling the shapes of single-metal nanocrystals, rigorous shape control of multimetal nanocrystals remains challenging, and has been limited largely to alloy systems of similar metals. Here we describe a robust strategy that produces shape-controlled intermetallic nanocrystals involving elements of notably different reduction potentials, reduction kinetics, and reactivity. The approach utilizes shape- and size-controlled β-Sn nanocrystals as reactive templates that can be converted into binary M-Sn (M = Fe, Co, Ni, Pd) intermetallic compounds by reaction with appropriate metal salt solutions under reducing conditions. The result, demonstrated in detail for the FeSn₂ system, is a variety of nanostructures with morphologies that include spheres, cubes, hollow squares, U-shaped structures, nanorods, and nanorod dimers. Our experiments demonstrate a size- and shape-dependent reactivity toward the formation of hollow FeSn₂ nanostructures and provide empirical guidelines for the formation of other intermetallic nanocrystals. In addition to those of FeSn₂, nanocrystals of intermetallic PdSn, CoSn ₃, and NiSn₃ can be formed using this same chemical conversion strategy.